Carolina Diaz

Amyloid fibrils may serve as building blocks for the preparation of novel hydrogel materials from abundant, low‐cost, and biocompatible polypeptides. This work presents the formation of physically cross‐linked, self‐healing hydrogels based on bovine serum albumin at room temperature through a straightforward disulfide reduction step induced by tris (2‐carboxyethyl) phosphine hydrochloride. The structure and surface charge of the amyloid‐like fibrils is determined by the pH of the solution during self‐assembly, giving rise to hydrogels with distinct physicochemical properties. The hydrogel surface can be readily functionalized with the extracellular matrix protein fibronectin and supports cell adhesion, spreading, and long‐term culture. This study offers a simple, versatile, and inexpensive method to prepare amyloid‐based albumin hydrogels with potential applications in the biomedical field.

The major fibronectin (FN) binding integrins α₅β₁ and α_vβ₃ exhibit cooperativity during cell adhesion, migration and mechanosensing, through mechanisms that are not yet fully resolved. Exploiting mechanically-tunable, nano-patterned substrates, and peptidomimetic ligands designed to selectively bind corresponding integrins, we report that focal adhesions (FAs) of endothelial cells assembled on integrin α₅β₁-selective substrates, rapidly recruit α_vβ₃ integrins, but not vice versa. Blocking of integrin α_vβ₃ hindered FA maturation and cell spreading on α₅β₁-selective substrates, indicating a mechanism dependent on extracellular ligand binding and highlighting the requirement of α_vβ₃ engagement for efficient adhesion. Recruitment of α_vβ₃ integrins additionally occurred on hydrogel substrates of varying mechanical properties, above a threshold stiffness supporting FA formation. Mechanistic studies revealed the need for soluble factors present in serum to allow recruitment, and excluded exogenous, or endogenous, FN as the responsible ligand for integrin α_vβ₃ accumulation to adhesion clusters. Our findings highlight a novel mechanism of integrin co-operation and the critical role for α_vβ₃ integrins in promoting cell adhesion on α₅β₁-selective substrates.

Device-related infections (DAI) remain a serious concern in modern healthcare. Bacterial attachment to a surface is the first step in biofilm formation, which is one of the main causes of DAIs. The development of materials capable of preventing or inhibiting bacterial attachment constitutes a promising approach to deal with this problem. The multifactorial nature of biofilm maturation and antibiotic resistance directs the research for multi-targeted or combinatorial therapeutic approaches. One attractive strategy is the modification or the engineering of surfaces in order to provide antiadhesive and/or antimicrobial properties. Currently, several different approaches that involve physical and chemical surface modification, deliver some possible alternatives to achieve this goal. The engineered surfaces can be coated with molecules capable of inhibiting the bacterial adhesion or with active agents that kill microorganisms. In addition, surfaces can also be modified in order to be stimuli-responsive, responding to a particular trigger and then delivering the consequent antimicrobial outcome. Here, we review the prevailing strategies to modify surfaces in order to create an antimicrobial surface and discuss how different surface functionalization can affect bacterial adhesion and/or viability.

The insertion and function of the muscle-type nicotinic acetylcholine receptor (nAChR) in Au(111)-supported thiolipid self-assembled monolayers have been studied by atomic force microscopy (AFM), surface plasmon resonance (SPR), and electrochemical techniques. It was possible for the first time to resolve the supramolecular arrangement of the protein spontaneously inserted in a thiolipid monolayer in an aqueous solution. Geometric supramolecular arrays of nAChRs were observed, most commonly in a triangular form compatible with three nAChR dimers of ∼20 nm each. Addition of the full agonist carbamoylcholine activated and opened the nAChR ion channel, as revealed by the increase in capacitance relative to that of the nAChR–thiolipid system under basal conditions. Thus, the self-assembled system appears to be a viable biomimetic model to measure ionic conductance mediated by ion-gated ion channels under different experimental conditions, with potential applications in biotechnology and pharmacology.

The aggregation behavior and morphological characteristics of amphiphilic block copolymer polybenzyl methacrylate-block-poly(dimethylamino)ethyl methacrylate (PBzMA-b-PDMAEMA) at the air–water interface were investigated through surface pressure measurements, atomic force microscopy (AFM) imaging, electrochemical measurements and X-ray reflectivity. Ionization of PDMAEMA blocks significantly affects the isotherms of the surface films at the air–water interface and, consequently, originates different morphologies of Langmuir–Blodgett films obtained under different experimental conditions. At low pH the PDMAEMA blocks are fully protonated and therefore dissolved in the aqueous subphase. Under this condition, the effects of the solubility and electrostatic repulsion of submerged PDMAEMA chains prevail over hydrophobic interactions and the Langmuir film exhibits low surface pressure at large molecular area values. Upon compression, the isotherm shows a pseudoplateau corresponding to the “pancake-to-brush” transition followed by an increase in surface pressure at smaller MMA values. These results were correlated with the morphological features of Langmuir–Blodgett films transferred onto silicon substrates, where dispersed dot-like domains that gradually transformed into an island-like structure, followed by further percolation into a continent-like morphology, were observed through AFM imaging. On the other hand, at high pH the isotherm is more expanded and the film exhibits higher surface pressure at relatively high MMA values due to the strong repulsive interactions between interface-confined hydrophobic aggregates constituted of PBzMA cores and neutral PDMAEMA shells. In this case, the AFM results show a structural evolution from circular and quasi-hexagonally packed micelles, followed by a worm-like structure that collapses into a homogeneous film. Furthermore, the study of the copolymer behavior under different subphase ionic strength conditions confirmed the critical role of electrostatic interactions in determining the characteristics of the isotherm. We could also demonstrate that our system follows accurately the scaling relationship for surface pressure of annealed brushes. Complementary studies performed by means of X-ray reflectivity were carried out to probe the buried interfacial structure of the diblock copolymer film, corroborating that the organization of both blocks on the silicon substrates is strongly dependent on the pH conditions of the subphase during the LB transfer.